This invention relates to the treatment of surface oxide layers on articles.
The invention finds particular application to the treatment of articles produced by casting, to treat surface oxide layers which are formed during the casting process.
In the production of articles by casting, surface oxide layers are often formed in the cast article by reaction of the casting material with the casting mould. Such layers are usually brittle and have to be removed to finish the article. It is sometimes possible to inhibit the formation of such layers by coating the interior surfaces of the moulds with an inhibiting material. However, with some casting materials (such as, for example, titanium) this may not be possible or not desirable in view of the increased cost involved, and in these cases the resultant oxide layers must be removed by chemical machining. Unfortunately, chemical machining destroys fine detail in the surface structure of the articles and so can only be used with articles which do not require high dimensional accuracy. For this reason it has been necessary, in order to produce articles of high dimensional accuracy in such materials as titanium, to mechanically machine the articles, thus resulting in high production costs.
It is an object of the present invention to provide a method of treating surface oxide layers on articles whereby the above disadvantages may be overcome or at least alleviated.
In accordance with the present invention a method of treating a surface oxide layer on an article comprises contacting the surface oxide to be treated with an oxygen scavenge agent and heat treating the article in an inert atmosphere for a sufficient time and at a sufficient temperature to cause the oxygen in the surface oxide layer to diffuse into the oxygen scavenge agent.